Communication line monitoring system

ABSTRACT

One or more lines of a communication terminal are monitored to determine blocked calls by detecting times of incoming calls. A signal corresponding to the pattern of incoming calls is generated from the detected times. After detection of the starting time of an all lines are busy state, an estimate of blocked calls is formed from the incoming call pattern signal and the detected start of the all lines are busy state.

FIELD OF THE INVENTION

The invention relates to monitoring of communication lines and, moreparticularly, to communication line monitoring arrangements adapted todetermine blocked calls to a communication terminal.

BACKGROUND OF THE INVENTION

As is well known in the art, monitoring communication parameters such asthe number of incoming and outgoing calls, holding time and lost callsat a communication terminal is needed to properly manage terminaloperations. While the information required for evaluating the operatingcondition of a communication terminal is available at a switching centerto which the lines of the terminal are connected, access to suchinformation may involve long delays. In order to improve efficiency andreduce cost, monitoring devices to automatically observe and record theactivity of lines at a communication terminal have been employed. Withthe line monitoring devices, the condition of the terminal and thecommunication line traffic may be ascertained in a timely fashionwithout requiring access to a switching center for information.

U.S. Pat. No. 4,712,230 issued Dec. 8, 1987 to J. E. Rice et al., forexample, discloses a programmable monitoring and recording apparatususable with any desired telephone set up in which an off-hook detectorand a line status unit provide line status signals to an indicatorpanel. The monitoring and recording apparatus is connected in parallelwith one or more telephones to record in memory and print out, for eachdetected call, information such as the number dialed, the time, date andduration of call, the station originating the call, the number of rings,whether destination busy and whether there was voice communication. Therecorded information on the operation of the telephone set up permitsadjustment and modification that improve telephone service on reviewingthe recorded information in a timely manner.

U.S. Pat. No. 4,270,024 issued May 26, 1981 to P. Theis et al. disclosesa telephone line activity monitor that utilizes a dedicated computer totabulate line traffic parameters. The monitor computer is adapted tostore and display preselected parameters as histograms and todiscriminate between incoming and outgoing calls based on the presenceor absence of a ring prior to a line going off-hook. Ringing isrecognized by measuring the frequency of major fluctuations in thesignal on the T-R pair of a telephone line.

Neither of the foregoing automatic monitoring arrangements that acquireinformation from the lines of a communication terminal detects ordetermines incoming calls to a communication terminal that are lost dueto all lines of the terminal being in a busy state. Such lost calls areblocked at a switching center which may be remotely located in atelephone central office. As a result, there is no indication of theblocked calls on the lines of the communication terminal. Suchinformation on blocked calls may be obtained from the connectedswitching center by manual inquiry or through the use of relativelyexpensive and complex circuit connections.

Soviet Union patent Document 1192162 dated Nov. 15, 1982 disclosesswitching apparatus that monitors lost telephone calls by measuring thenumber of calls being serviced on every occasion when a call loss isdetermined. The loss criterion is calculated at the end of a prescribedtime interval as a function of the number of calls at the time of eachcall loss and the number of call losses. The arrangement providesautomatic monitoring of the condition of a system and measurement of thestatistical characteristics of telephone call transmission. Accuracy isimproved by taking into account all calls in analysis. The monitoringrequires detection of lost calls. As aforementioned, such lost callinformation is available at switching centers but cannot be obtained bymonitoring telephone lines.

Thus, it is a problem of communication terminal management that blockedcall information is not available in a timely fashion and that blockedcall information is not available through automatic monitoring ofcommunication terminal lines.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide information onblocked calls to a communication terminal by automatic monitoring of thelines of the terminal.

It is another object of the invention to provide an estimate of blockcalls in a communication terminal using a calling pattern of incomingcalls to monitored lines of a communication terminal.

The invention is directed to a communication system having at least onecommunication line in which the times of incoming calls are detected anda signal corresponding to a calling pattern of incoming calls isgenerated from the detected incoming call times. The starting time of astate in which all communication lines are busy is detected and anestimate of incoming call blockage is formed on the basis of the busystate starting time and the calling pattern signal.

According to one aspect of the invention, the times of incoming callsare detected over a prescribed time interval and the calling patternsignal is formed from the times of incoming calls over the prescribedtime interval.

According to another aspect of the invention, the prescribed timeinterval is related to the holding times of incoming calls.

According to yet another aspect of the invention, the calling patternsignal corresponds to the times successive incoming calls are initiatedover the prescribed time interval.

According to yet another aspect of the invention, the calling patternsignal corresponds to a statistical parameter related to differencebetween the times at which successive incoming calls are initiated overthe prescribed time interval.

According to yet another aspect of the invention, a signal representingan estimate of blocked calls is formed by combining the differencebetween the time at which at least one communication line is releasedfrom its busy state after all communication lines have been in the busystate and the starting time of the state in which all communicationlines are busy with the calling pattern signal.

According to yet another aspect of the invention, an alarm signal isgenerated on the basis of the start time of the all lines are busy stateand calling pattern signal for incoming calls.

According to yet another aspect of the invention, an alarm signal isgenerated when the average time difference between initiation ofsuccessive incoming calls over the prescribed time interval elapsessubsequent to the starting time of the all lines are busy state.

In an embodiment illustrative of the invention, lines of a communicationterminal are periodically scanned through line monitoring interfacecircuits to detect line hook states. The line hook states are stored andtimes at which incoming calls on selected lines are initiated aredetected in a signal processor from the stored line hook states. Whenthe start of an all lines are busy state is detected by processoranalysis of stored line hook states, a signal corresponding to theaverage of differences in initiation times of successive calls over aprescribed time interval is formed. An alarm is set upon elapse ofaverage initiation time difference subsequent to the start of the alllines busy state. Upon determination of the termination of the all linesbusy state in the processor when a line goes on hook, a signalcorresponding to an estimate of blocked calls is generated on the basisof the period of the all lines are busy state and the average differencein incoming call initiation times over the prescribed time interval.

The invention will be better understood from the following more detaileddescription taken with the accompanying drawings and claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an embodiment of an automatic monitoringsystem for a communication terminal that is illustrative of theinvention.

FIG. 2 is a schematic diagram of a line interface circuit useful in theembodiment of FIG. 1;

FIG. 3 is a more detailed block diagram of the embodiment depicted inFIG. 1;

FIG. 4 is a flow chart illustrating the general operation of theembodiment depicted in FIG. 1;

FIG. 5 is a more detailed flow chart illustrating the timer processingin the flow chart of FIG. 4;

FIG. 6 is a more detailed flow chart illustrating the scan keysprocessing in the flow chart of FIG. 4;

FIG. 7 is a more detailed flow chart illustrating the line statusprocessing in the flow chart of FIG. 4; and

FIG. 8 is a more detailed flow chart illustrating the estimated blockedcall processing and alarm signal forming operations of the flow chart ofFIG. 4.

DETAILED DESCRIPTION

FIG. 1 is a general block diagram of an automatic monitoring systemillustrative of the invention. For purposes of illustration, it isassumed that a 24 line telephone system is monitored. It is to beunderstood, however, that telephone systems having a different number oftelephones, communication systems with telephones and data units such asfacsimile devices or modems, or other types of communication systems maybe monitored in accordance with the invention.

Referring to FIG. 1, there is shown a switching center 101 which may bea remotely located centrex, telephone lines 105-1 to 105-24, telephones103-1 to 103-24, line interface circuits 110-1 to 110-24, a buffer 112to isolate line interface circuits 110 to 110-24, a processor 120 whichmay comprise a Z-80 microprocessor or other microprocessor andassociated memory and interface arrangements, a printer 125 which may bea dot-matrix type and an indicator panel 130 which may include an LCDpanel well known in the art. The display panel includes a display 131, atelephone activity unit 133, a keypad 135 and an operation key unit 137.While telephones 103-1 to 103-24 are shown in FIG. 1, it is to beunderstood that each line of lines 105-1 through 105-24 may be connectedto a facsimile device, a modem or another type of communication device.

The switching center 101 is coupled to telephones 103-1 to 103-24through lines 105-1 to 105-24, respectively, and inputs of lineinterfaces 110-1 to 110-24 are coupled to lines 105-1 to 105-24 throughinterface lines 107-1 to 107-24, respectively. Such coupling may includecoupling through standard telephone connectors. Outputs of lineinterfaces 110-1 to 110-24 are coupled to inputs of the buffer 112 andan output of the buffer 112 is coupled an input of the processor 120through a line. An output of the processor 120 is coupled to the display131 of the indicator panel 130. The telephone line activity unit 133 iscoupled through a line to the processor 120. The keypad 135 is coupledthrough another line to an input of the processor 120. the operation keyunit 137 is coupled through another line to the processor 120 and theprinter 125 is coupled to the processor 120 through yet another line.

Operation of the monitor system of FIG. 1 is initiated after it isturned on by depressing a date/time key 137-6 and entering the timeinformation by setting the date and time with keys of the keypad 135. Atime period for monitoring is then set using a period start/stop key137-8 and keys of the key pad 135. After the monitoring period has beenset, a set active lines key 137-7 is depressed and lines to be monitoredare selected using the keypad 135. Subsequent to active line selection,selected line LEDs of line activity unit 133 display the lines beingmonitored.

During operation of the monitor apparatus of FIG. 1, the selected lineinterface circuits 110-1 to 110-24 detect and monitor the hook states ofthe lines connected thereto. As is well known in the art, the DC voltagebetween ring and tip conductors of a telephone line exceeds 40 voltswhen the line is on-hook. In a typical telephone system in the UnitedStates If a telephone or other communication device connected to theline goes off-hook, the voltage between ring and tip conductorsdecreases to less than 10 volts DC. During a ringing signal, thedifferential voltage between ring and tip alternates between the on-hookand off-hook voltages at a maximum rate of 5 Hz. Each line interface(e.g., interface 110-1) detects the hook state of the connected line(e.g. line 105-1) and converts the hook signal on the line to acorresponding hook-state logic signal as will be described. When atelephone (e.g., 103-1) is on-hook, a logic 1 signal is output from thecorresponding line circuit. A logic 0 signal is obtained when atelephone is off-hook and alternating logic is and logic 0s are obtainedwhen a line is in a ringing state. It is to be understood, however, thatother types of interface circuits well known in the art may be used togenerate the hook state signals where the line signaling arrangementsdiffering from those described are employed.

The processor 120 in FIG. 1 is adapted to receive the hook state signalsfrom the line interfaces 110-1 to 110-24 through buffer 112 and toperiodically scan the hook state logic signals obtained from the lineinterfaces at a prescribed times (e.g. every 8 milliseconds). Bycomparing the present hook state logic signal with the immediatelypreceding hook state logic signal, a determination is made as to theline status. A count of the time that a line is off-hook and a count ofhook state toggling are also maintained. When a line is on-hook, thehook count is zero and the toggle count is zero. An off-hook linescanned at 8 millisecond intervals provides a hook count of 125 everysecond. If a line is in a ringing state, the hook state will alternateevery 8 milliseconds and a comparison between present and immediatelypreceding hook states provides a toggle count indicative of the ringingstate.

As a result of the analysis in the processor 120 of the hook state, hookcount and toggle count signals, the line status is determined as anincoming, an outgoing, a lost or a no-call. An incoming call is detectedwhen a ring state is followed by an off-hook state. An outgoing call isdetected when an on-hook state is followed by an off-hook state. A lostcall is detected when a ring state is followed by an on-hook state and ano call state corresponds to a detected ring state. The no call statebecomes an incoming call when the line goes off hook from the ring stateand becomes a lost call when the line goes on hook from the ring state.

The processor 120, as will be described in greater detail, scans theoutputs of the line interfaces 110-1 to 110-24 for hook states every 8milliseconds and generates signals corresponding to the status of eachactive line as to incoming calls, outgoing calls, and lost calls andsignals as to call holding time (i.e., duration of an incoming call)every second. The line status information is stored for a period set byoperation of a period start/stop key 137-8 or a most recent period key137-9 and keypad 135. The number of incoming, outgoing or lost calls orthe average call holding time may be recalled from storage and displayedon the LCD display 131 by depressing the appropriate one of incomingcalls key 137-1, outgoing calls key 137-2, lost calls key 137-3 or ave.hold key 137-5.

In addition to monitoring the status of each selected line, the circuitof FIG. 1 is also adapted to determine the estimated busy timecorresponding to an estimate of blocked calls by monitoring thecommunication lines 105-1 through 105-24 and to set an alarm when ablocked call is expected. A blocked call corresponds to a call thatcannot be completed because all lines are in a busy state. As is wellknown, it is not possible to detect a blocked call by line hook statemonitoring since the call is blocked at a switching center prior toreaching the lines. The blocked call information is only available atthe remotely located switching center 101. According to the invention, asignal corresponding to an accurate estimate of blocked calls isproduced by determining a calling pattern of incoming calls solely fromthe monitored line hook states at the communication terminal. As aresult, it is automatically determined when blocked calls are likely tooccur in real time. The monitoring requires only coupling to thecommunication lines of the terminal and is non-invasive in avoidingspecial lines between the switching center and the terminal dedicated todetermining blocked calls or other terminal conditions. The terminaloperation may then be adjusted accordingly from the blocked calldetermination performed only at the terminal.

According to the invention, blocked incoming calls due to all lines of acommunication system being busy is estimated by determining the averagerate of incoming calls, determining the time interval in which all linesare busy (i.e., in use) and calculating an estimate of the number ofblocked calls from the determined average incoming call rate and thetime interval in which all lines are in use. The rate of incoming callscorresponds to a calling pattern and the time interval in which alllines are in use corresponds to a state in which all lines are busy.

In the illustrative embodiment shown in FIG. 1, a calling pattern signalis generated by detecting the times at which incoming calls areinitiated over a prescribed time interval I and forming a call patternsignal TAV representing the average of the differences betweeninitiation times (e.g. t1, t2, . . . , tn, . . , tN) of the N successiveincoming calls in the interval I. When at a time TAOFF an all lines arebusy state is detected as a result of scanning the active line interfacecircuits 110-1 to 110-24, a signal corresponding to a predeterminedmultiple of the average incoming call holding time over the presetmonitoring period is generated from the line status signals stored inthe processor 120 to provide the prescribed time interval. It is to beunderstood, however, that the prescribed time interval may be fixedperiod (e.g., 10 minutes) or determined according to otherconsiderations.

Once the prescribed time interval signal I is generated, signalsrepresenting the differences between starting times of the successiveincoming call (e.g., tn-tn-1) in the prescribed time period are producedin the processor 120 from stored line status signals. The call patternsignal TAV is formed according to the relationship ##EQU1## where N isthe total number of incoming calls in the prescribed time interval and ncorresponds to the nth successive incoming call in the prescribed timeinterval. An alarm signal may be set at a time TAOFF+TAV. It is to beunderstood, however, that other statistical parameters derived from thecalling pattern may also be employed.

When a line going on-hook at a time TONH is detected, the state in whichall lines are off-hook is terminated and an estimated blocked callsignal EBC is generated in the processor 120 according to therelationship

    EBC=(TONH-TAOFF)/TAV                                       (2)

corresponding to the difference between the start and the terminationtimes of the all lines busy state modified by the calling patternsignal. The estimated blocked call signal may be displayed on the LCDdisplay 131 by depressing an estimated busy key 137-4 of the operationkey unit 137. While an average of the initiation time differences forincoming calls is used in the illustrative embodiment shown in FIG. 1,it is to be understood that other signals representative of callingpatterns for incoming calls may be utilized.

With respect to equation 2, the difference between the termination timeTONH and the starting time TAOFF represents the blocking time and thecall pattern signal is representative of the rate at which incomingcalls occur just prior to the start of the blocking time. As is readilyseen from equation 2, the number of blocked calls is proportional to theblocking time and inversely proportional to the rate of incoming calls.I have found that this relationship provides an accurate estimate of thenumber of blocked calls at a communication terminal and can be used withstandard calculations to determine the number of additional linesrequired at the terminal to prevent blockage.

Advantageously and in accordance with the invention, the number ofblocked calls is accurately estimated in real time by non-invasivelymonitoring only the hook states of the communication terminal lines andthere is no need for additional lines from a switching center to thecommunication terminal to transmit information concerning blocked calls.As is well known in the art, the total traffic in the busy hourcorresponds to the product of the average holding time, 0.6 CCS and sumof the number of incoming calls, the number of outgoing calls, theestimated number of blocked calls and the number of lost calls. Thenumber of lines required to handle the call traffic load is the totaltraffic in CCS divided by 36. Consequently, line traffic management canbe performed at the communication terminal without reference to blockedcall information from the remote switching center.

The signal pattern signal TAV in the illustrative embodimentcorresponding to the average difference between starting times ofsuccessive incoming calls represents the time at which the next incomingcall is expected. Thus, according to one aspect of the invention, analarm signal is generated after a time TAV subsequent to the initiationof a detected all lines busy state. According to this aspect of theinvention, an automatic indication of blocked calls is provided so thatthe operation of the communication signal may be immediately adjusted.

FIG. 2 depicts a more detailed block diagram of a line interface circuit(e.g. 110-1) of FIG. 1. Referring to FIG. 2, there is shown a portion ofan interface line 107-1, a bridge rectifier 201 having a pair of inputsand a pair of outputs, a differential operational amplifier 220 having apositive input, a negative input and an output, a Schmidt triggerinvertor 230 having an input and an output, a resistive-capacitivenetwork including coupling resistors 203 and 205 and a capacitor 207, avoltage divider network including a variable resistor 213, a fixedresistor 215 and a fixed resistor 217, an operational amplifier feedbackresistor 209 and a low pass filter including a resistor 222 and acapacitor 224.

The input terminal pair of the bridge rectifier 201 is coupled to theinterface line 107-1. The resistor 203 is coupled between an output ofthe bridge rectifier 201 and the positive input of the operationalamplifier 220 and the resistor 205 is coupled between another output ofbridge rectifier 201 and the negative input of operational amplifier220. The capacitor 207 is coupled between the positive input ofamplifier 220 and the negative input of amplifier 220. A terminal of thevariable resistor 213 is connected to a positive voltage terminal andanother terminal of the resistor 213 is connected to the junction of thepositive input of the amplifier 220 with the resistor 203.. A terminalof the resistor 209 is connected to the output of the amplifier 220 andanother terminal of resistor 209 is connected to the input of theamplifier 220.

A terminal of the resistor 217 is connected to another positive voltageterminal and another terminal of the resistor 217 is connected to thenegative input of the amplifier 220. A terminal of the resistor 215 isconnected to the negative input of the amplifier 220 and anotherterminal of the resistor 215 is connected to a reference potential(e.g., ground). A terminal of the resistor 222 is connected to theoutput of the amplifier 220 and another terminal of the resistor 222 isconnected to the input of the Schmidt trigger 230. A terminal of thecapacitor 204 is connected to the input of the Schmidt trigger 230 andanother terminal of the capacitor 204 is connected to the referencepotential (e.g., ground). The output of the Schmidt trigger 230 isconnected to a line 235.

In operation, the voltage on line 107-1 representative of the hook stateof the communication line connected thereto is supplied to the inputterminal pair of the bridge rectifier 201 and the rectified output fromthe bridge rectifier 201 is coupled by the resistive-capacitive networkincluding resistors 203 and 205 and capacitor 207 to the positive andnegative inputs of the amplifier 220. The use of the bridge rectifierpermits connection of the interface circuits to communication lines withnormal or reverse tip and ring connections. Voltage divider resistor 213is adjusted to obtain a desired DC operating voltage for properdetection of on-hook and off-hook states by the Schmidt trigger invertor230 and the values of the resistors 203, 205, 213, 215 and 217 areselected as is well known in the art to provide a high input impedanceas required by FCC regulations.

The output of amplifier 220 corresponding to the hookstate of themonitored line is low pass filtered by the arrangement of the resistor222 and the capacitor 224 to remove unwanted noise from the input of theSchmidt trigger invertor 230. The Schmidt trigger invertor 230 producesa logic signal corresponding to the hook state of the monitored line.The output of the Schmidt trigger invertor 203 is a logical 1 when themonitored line is on-hook and a logical 0 when the monitored line isoff-hook. The output of the Schmidt trigger invertor 230 is analternating logical 1 and a logical 0 when the line to which theinterface circuit is connected is in a ringing state. The hook statelogical signal at the output of Schmidt trigger invertor 230 is appliedto an input of the buffer 112 in FIG. 1 via the line 235.

FIG. 3 shows a more detailed block diagram of the processor 120 of FIG.1 together with other circuits of FIG. 1. Referring to FIG. 3, there isshown line interfaces 110-1 to 110-24, the buffer 112, the printer 125,the LED display 131, the line activity unit 133, the keypad 135, theoperation key unit 137, an alarm latch and indicator 338 and theprocessor 120. The processor 120 includes a microprocessor 322 which maybe a Z-80 microprocessor or any other microprocessor adapted to performthe functions illustrated in the flow charts of FIGS. 4 through 8, arandom access memory (RAM) 324 to store data, a read only memory (ROM)326 to store control instruction signals, an input-output interface 328,and a bus 329.

As aforementioned with respect to FIG. 1, inputs of line interfaces110-1 to 110-24 are coupled to the tip and ring conductors ofcommunication lines 105-1 to 105-24 and are indicated as coupled to tipT and ring R conductors of communication terminal lines in FIG. 3.Outputs of line interfaces 110-1 to 110-24 are coupled to inputs of thebuffer 112. The microprocessor 322, the RAM memory 324 and the inputoutput interface 328 are coupled to the common bus 329 throughbidirectional lines and the ROM 326 is coupled to the common bus 329through a unidirectional line. The input-output interface 328 is coupledvia a line to the printer 125, via lines to latches 335-1 through 335-24of the line activity unit 133, via another line to display 131 andthrough yet another line to the alarm latch and indicator 338. Latches335-1 to 335-24 are coupled through lines to LEDs 333-1 to 333-24,respectively.

The ROM 326 has stored therein instruction signals that control theoperation of the processor 120. These instruction signals correspond tothe operations shown in the flow charts of FIGS. 4-8 and are arranged tocontrol the microprocessor 322, the RAM 324 and the input outputinterface 328 to carry out the operations illustrated in the flow chartsof FIGS. 4-8.

FIG. 4 is a flow chart illustrating the general operation of theembodiment of the invention. Referring to the block diagram of FIG. 3and the flow chart of FIG. 4, a timer signal is set initially set tozero in a step 401 and an operating loop including steps 410 through 435is entered from the step 401 periodically at preset times (e.g., every 8milliseconds). In step 410, timer processing is performed that includesscanning the active lines and updating the hook count and toggle countfor each line based on the scanned hook states at the preset interrupts.

The timer processing is shown in greater detail in the flow chart ofFIG. 5. Referring to FIGS. 3 and 5, a step 501 is entered from theoutput of step 401 in FIG. 4 and the timer signal is incremented by 8milliseconds. Control is passed to a step 505 in which hook state dataobtained from line interfaces 110-1 to 110-24 through the buffer 112 andthe interface 328 and stored in the RAM memory 324 is accessed by themicroprocessor 322 in FIG. 3. Next, a line index i is set to zero in astep 510 and the loop from a step 515 to a step 545 is initiallyentered. In the decision step 515, the value of the line index i ischecked to determine if all lines have been processed.

Until the index i is greater than 24, the lines are sequentiallyprocessed in the loop from step 515 to 545. In the timer processingillustrated in FIG. 5, the hook state logic signals from line interfaces110-1 to 110-24 are transferred to the processor 120 via the buffer 112and Whether or not line i is off-hook is determined in a decision step520. If line i is off-hook, the hook count stored in RAM memory 324 forline i is incremented in the microprocessor 322 (step 525) and returnedto the RAM memory 324. A decision step 530 is then entered. Otherwise,the decision step 530 is entered directly from the "NO" output of thedecision step 520. The presently scanned hook state is compared to thehook state scanned in 8 milliseconds preceding the present scan in thedecision step 530. If the present hook state is different from thepreceding hook state indicating ringing, the toggle count stored in RAMmemory 324 is incremented in a step 535.

A step 540 is then entered in which an LED corresponding to the line iis set to display the hook status of the line. When the line isdetermined to be off-hook in microprocessor 322, a signal from themicroprocessor is sent to the corresponding line latch (e.g., latch335-1 in FIG. 3) and an LED for the line (e.g., LED 333-1) is turned on.If the line is determined to be on-hook, the latch is reset and the LEDfor the line is turned off. After the display update in the step 540,the line index i is incremented in a step 545.

The operations of the loop from the step 515 to the step 545 areiteratively performed until the hook status, the hook count and thetoggle count for each line is determined in the microprocessor 322 andstored in the RAM memory 324. When the line index i exceeds 24, controlis returned to a decision step 415 in FIG. 4 from the "NO" output ofstep 515 and it is determined whether the timer signal value is amultiple of 128 milliseconds. Until the timer signal value reaches thenext multiple of 128 milliseconds, the timer processing is repeatedevery 8 milliseconds as indicated in the step 410.

Every 128 milliseconds, a step 420 is entered from the "YES" output of adecision step 415 in FIG. 4 and scan key processing shown in greaterdetail in FIG. 6 is performed. During the scan key processing of FIG. 6,communication parameters are selectively displayed for the presetmonitoring period.

Referring to FIG. 6, a decision step 601 is entered from the step 415 ofFIG. 4. In the decision step 601, the microprocessor 322 determines if akey of operation key unit 137 corresponding to a condition beingmonitored has been depressed. If no operation key has been depressed,control is passed back to decision step 425 in FIG. 4. Otherwise, thestart and stop times of the monitoring period are obtained from RAMmemory 324 in a step 605. It is determined whether all lines or selectedlines are to be processed for display in a step 610. Depression of the *key causes a step 620 to be entered from the step 610 so that all linesare selected. In the absence of an * key signal, the active lines storedin the RAM memory 324 are selected. In either event, steps 625 to 680are then sequentially operated to selectively display communicationparameters.

If display of outgoing calls for the designated period is requested bydepressing the outgoing calls key 137-2 in FIG. 1 (step 625), themicroprocessor 322 searches the RAM memory 324 for outgoing call dataand stores the result in the RAM memory 324 (step 630). When display ofincoming calls is requested by depressing the incoming calls key 137-1(step 635), incoming call data in RAM memory 324 is obtained and theresulting number of incoming calls is stored in the RAM memory 324 (step640). Similarly, the number of lost calls in the prescribed period maybe requested (step 645) and the number of lost calls for the period istotaled and stored in RAM memory 324 (step 650).

When the ave. hold key 137-5 is depressed, step 660 is entered from thedecision step 655 in which call holding data is obtained for theprescribed period from the RAM memory 324. A signal representing theaverage call holding time for the period is then produced in themicroprocessor 322 and stored in the RAM memory 324 (steps 660 and 665).The estimated number of blocked calls for the prescribed period storedin the RAM 324 may also be displayed by depressing the EST. BUSY key137-4 to access the estimated blocked call signal stored in RAM 324through steps 670 and 675. The selected data to be displayed istransferred from the RAM memory 324 to the display 131 as per step 680and control is thereafter passed to the instruction signals stored forthe decision step 425 in FIG. 4.

The decision step 425 normally returns the monitor operation to thetimer processing step 410. Every second, the normal path is interruptedand a step 430 in which line status processing is performed to obtainline status parameters with a resolution of 1 second. The line statusprocessing which includes detecting and recording information onincoming, outgoing and completed calls as well as call holding time andbusy calls is shown in greater detail in the flow chart of FIG. 7.

Referring to FIG. 7, a step 701 is entered from the step 425 of FIG. 4at intervals of one second (i.e., one second interrupt) and a line indexis set to 1 to address hook related information for the addressed linestored in the RAM memory 324. Whether the currently addressed line isactive is then determined in a decision step 703. If the addressed lineis active, a check is made as to whether the line is on-hook in a step705. When the addressed line is found to be on-hook, a check as towhether the line was in a ringing state at the previous one secondinterrupt is made in the microprocessor 322 from data in the RAM memory324 (step 707). If the addressed line is now on-hook and was previouslyringing, a lost call for the addressed line is recorded in the RAMmemory 324 in a step 709. A decision step 711 is then entered in whichit is determined if the addressed line was off-hook at the preceding onesecond interrupt. If the change from off-hook to on-hook status isdetermined in the microprocessor 322 (step 711), a completed call andthe time of call completion is stored in the RAM memory 324 (step 713).

When an active line is determined as not on-hook in the step 705,control is transferred to stored instruction signals in ROM memory 326corresponding to a decision step 715. In the step 715, whether theaddressed line is off-hook is checked. When the addressed line is foundto be off-hook, it is determined if the addressed line was on-hook atthe preceding one second interrupt (step 718). A change from on-hook tooff-hook status causes an outgoing call to be recorded in the RAM memory326 in a step 720. If, however, the line was ringing at the precedingone second interrupt (step 722) and is now off-hook (step 715), anincoming call and its starting time are recorded for the addressed linein the RAM memory 324 (step 725). A decision step 728 is entered fromeither the decision step 722 or the step 725 and a check of whether theline was off-hook at the preceding one second interrupt is made. If a"YES" decision is made, the holding time is incremented and stored inthe RAM memory 324 in a step 730.

In the event the addressed active line is determined not in the on-hookstate in the step 703 and not in the off-hook state in the step 715, theaddressed line is checked for ringing state status in a step 733. Whenfound to be in the ringing state in the step 733, it is determinedwhether the addressed line was on-hook at the preceding one secondinterrupt. If so, a new busy line signal is generated in themicroprocessor 322 and stored in the RAM memory 324. At the end of linestatus determination, a step 742 is entered from the step 711, 713, 728,730, 736 or 739 in which the line number is incremented so that the linestatus processing can be performed for the succeeding line. Whether alllines have been processed is determined in a decision step 746. If not,the step 703 is reentered. After all lines have been processed accordingto the flow chart of FIG. 7, the hook count and toggle count signals arereset in a step 750. The instruction signals in ROM 326 then passcontrol to a step 435 of FIG. 4 wherein blocked calls are estimatedblocked call and alarm processing are performed.

FIG. 8 is a flow chart showing the blocked call estimation and alarmprocessing in greater detail. Referring to FIG. 8, a decision step 801is entered from the step 430 of FIG. 4 and the microprocessor 322 checksthe data in RAM memory 324 to determine if all lines are off-hook. Ifnot, the step 401 of FIG. 4 is reentered and the timer processing isrestarted. When an all lines busy state is detected in the step 801, thestarting time TAOFF of the all lines are busy state is stored in RAMmemory 324 (step 805) and a signal corresponding to the average holdingtime for the presently set monitoring period is generated from theholding time information stored in RAM 324 (step 807). A prescribed timeinterval I corresponding to a multiple (e.g. 5) of the average holdingtime is then formed in a step 810.

Upon determination of the prescribed time interval I in the step 810, Astep 815 is entered wherein the microprocessor retrieves the startingtimes of all incoming calls from RAM memory 324 for the prescribed timeinterval ending at the time TAOFF. The average signal TAV whichrepresents the incoming call pattern is then formed according toequation 1 in step 820 and the hook state signals stored in the RAMmemory 324 are scanned to determine if a line goes on-hook (step 825).

At each determination that all lines are off-hook in the step 825, adecision step 840 is entered to check whether the time TAV has elapsedfrom the time TAOFF at which the all lines busy state was detected. Thetime TAV corresponds to the time at which another incoming call isexpected to start. Since all lines are off-hook, such an incoming callcannot be served and a "YES" decision in the step 840 causes an alarmsignal to be generated in the microprocessor 322 (step 845). The alarmsignal is sent to the latch and indicator 338. Step 825 is reenteredfrom either step 840 or 845. Upon detection of a line going on-hook inthe step 830, the time TONH at which the line goes on-hook is set and anestimated blocked call signal is generated according to equation 2 in astep 835.

Assume, for purposes of illustration of the formation of the estimatedblocked call signal, that lines 105-1 to 105-5 are active in the monitorarrangement of FIG. 1, the average holding time of a call is 74 seconds,and the all lines are busy state is initiated at a time 10:05:12. Aprescribed time interval I is set to 370 seconds (step 810)corresponding to five times the average holding time. Further assumethat the starting times of all calls in the 370 seconds just prior tothe time tAOFF=10:05:12 are t1=10:02:16, t2=10:03:40, t3=10:04:10,t4=10:04:15, t5=10:04:18 and t6=10:05:12. The time between the start ofthe first and second incoming calls is t2-t1=84 seconds. The timebetween the start of the second and third calls is t3-t2=30 seconds. Thetime between the start of the third and fourth calls is t4-t3=5 secondsand the time between the start of the fourth and fifth calls is t5-t4=3seconds.

As a result of the determination in the step 820, the average timebetween incoming call starts over the prescribed time interval of 370seconds is TAV=30.5 seconds according to equation 1. An alarm signal isgenerated in the step 845 at time 10:05:43 to indicate that a blockedcall is estimated to have occurred. If one of the lines 105-1 to 105-5goes on hook at time TONH=10:06:50, the duration of the all lines arebusy state is 98 seconds and the estimated blocked calls signaldetermined from equation 2 is 3.2.

In accordance with the invention, the number of blocked calls isautomatically determined in real time and an alarm is generated when ablocked call is expected by monitoring hook states of the lines of acommunication terminal.

It is to be understood that the specific embodiment described herein ismerely illustrative of the spirit and scope of the invention.Modifications can readily be made by those skilled in the art inaccordance with the principles of the invention.

What is claimed is:
 1. A communication system having one or morecommunication lines comprising:means for detecting times of incomingcalls on at least one of the one or more communication lines; meansresponsive to the detected times of the incoming calls for generating asignal corresponding to a calling pattern of incoming calls; means fordetecting a time at which a state in which all communication lines arebusy is initiated; and means responsive to the detected initiation timeof the all communication lines busy state and the calling pattern signalfor forming a signal representative of blocked incoming calls.
 2. Acommunication system according to claim 1, wherein the means fordetecting the times of the incoming calls comprises:means fordetermining a prescribed time interval; and means for detecting thetimes of the incoming calls in the prescribed time interval.
 3. Acommunication system according to claim 2, wherein the means fordetermining the prescribed time interval comprises:means for generatinga signal corresponding to an average holding time of the incoming calls;and means responsive to the average holding time of the incoming callsfor setting the prescribed time interval.
 4. A communication systemaccording to claim 3, wherein the prescribed time interval is set to apredetermined multiple of the average holding time of the incomingcalls.
 5. A communication system according to claim 2, wherein the meansfor detecting the times of the incoming calls comprises means fordetecting the times at which the incoming calls are initiated in theprescribed time interval.
 6. A communication system according to claim5, wherein the means for generating the calling pattern signal comprisesmeans for forming a signal corresponding to the differences ininitiation times of the successive incoming calls in the prescribed timeinterval.
 7. A communication system according to claim 6, wherein thecalling pattern signal generating means further comprising meansresponsive to the initiation time differences signal for generating asignal representative of a statistical parameter of the initiation timedifferences in the prescribed time interval.
 8. A communication systemaccording to claim 7, wherein the statistical parameter signal is anaverage of the initiation time differences in the prescribed timeinterval.
 9. A communication system according to claim 1 furthercomprising:means for detecting a time at which the all communicationlines busy state is terminated; and the blocked incoming calls signalforming means comprises means responsive to the difference between theinitiation and termination times of the all communication lines busystate and the calling pattern signal for generating a signalcorresponding to a number of the blocked calls.
 10. A communicationsystem according to claim 9, wherein the number of blocked call signalgenerating means comprises means for forming a signal representing thedifference between the initiation and termination times of the allcommunication lines busy state divided by the calling pattern signal.11. A communication system according to claim 10, wherein the means fordetecting the times of the incoming calls comprises:means fordetermining a prescribed time interval; and means for detecting thetimes of the incoming calls in the prescribed time interval.
 12. Acommunication system according to claim 11, wherein the means fordetecting the times of the incoming calls in the prescribed timeinterval comprises means for detecting the times at which the incomingcalls are initiated in the prescribed time interval.
 13. A communicationsystem according to claim 12, wherein the means for generating thecalling pattern signal comprises means for forming a signalcorresponding to the differences in the detected initiation times ofsuccessive ones of the incoming calls in the prescribed time interval.14. A communication system according to claim 13, wherein the means forforming the initiation time differences signal comprises means forforming a signal representative of an average of the initiation timedifferences in the prescribed time interval.
 15. A communication systemaccording to claim i, further comprising means coupled to the one ormore communication lines for generating line status signals, and whereinthe means for detecting the initiation time of the state in which allcommunication lines are busy and the incoming call time detecting meansare responsive solely to the generated line status signals.
 16. Acommunication system having one or more communication linescomprising:means for detecting times of incoming calls on at least oneof the one or more communication lines; means responsive to the detectedtimes of the incoming calls for generating a signal corresponding to acalling pattern of incoming calls; means for detecting a time at which astate in which all communication lines are busy is initiated; and meansresponsive to the detected initiation time of the all communicationlines busy state and the calling pattern signal for forming a signalrepresentative of a time of occurrence of a blocked call.
 17. Acommunication system according to claim 16, wherein the means fordetecting the times of the incoming calls comprises:means fordetermining a prescribed time interval; and means for detecting thetimes of incoming calls in the prescribed time interval.
 18. Acommunication system according to claim 17, wherein the means fordetecting the times of the incoming calls comprises means for detectingthe times that incoming calls are initiated in the prescribed timeinterval.
 19. A communication system according to claim 18, wherein themeans for generating the calling pattern signal comprises means forforming a signal corresponding to differences in initiation times of thesuccessive incoming calls in the prescribed time interval.
 20. Acommunication system according to claim 19 further comprising meansresponsive to the initiation time differences signal for generating asignal representative of a statistical parameter of the initiation timedifferences in the prescribed time interval.
 21. A communication systemaccording to claim 20, wherein the statistical parameter signal is anaverage of the initiation time differences in the prescribed timeinterval.
 22. A communication system according to claim 20, wherein themeans for forming the signal representative of the time of occurrence ofa blocked call comprises means for generating a signal at a timecorresponding to the average of the initiation time differences in theprescribed time interval after the detected initiation of the allcommunication lines busy state.
 23. A communication system according toclaim 16, wherein the means for forming a signal representative of thetime of occurrence of a blocked call comprises means for generating asignal at a time corresponding to a value of the calling pattern signalafter the detected initiation of the all communication lines busy state.24. A communication system according to claim 16, further comprisingmeans coupled to the one or more communication lines for generating linestatus signals, and wherein the means for detecting the initiation timeof the state in which all communication lines are busy and the incomingcall time detecting means are responsive solely to the generated linestatus signals.
 25. A method for monitoring a communication systemhaving one or more one communication lines comprising the stepsof:detecting times of incoming calls on at least one of the one or morecommunication lines; generating a signal corresponding to a callingpattern of incoming calls responsive to the detected times of theincoming calls; detecting a time at which a state in which allcommunication lines are busy is initiated; and forming a signalrepresentative of blocked incoming calls responsive to the detectedinitiation time of the all communication lines busy state and thecalling pattern signal.
 26. A method according to claim 25, wherein thestep of detecting the times of the incoming calls comprises:determininga prescribed time interval; and detecting the times of incoming calls inthe prescribed time interval.
 27. A method according to claim 26,wherein the step of determining the prescribed time intervalcomprises:generating a signal corresponding to an average holding timeof the incoming calls; and setting the prescribed time intervalresponsive to the average holding time of the incoming calls.
 28. Amethod according to claim 27, wherein the prescribed time interval isset to a predetermined multiple of the average holding time of theincoming calls.
 29. A method according to claim 26, wherein the step ofdetecting the times of the incoming calls comprises detecting the timesat which incoming calls are initiated in the prescribed time interval.30. A method according to claim 29, wherein the step of generating thecalling pattern signal comprises forming a signal corresponding todifferences in initiation times of the successive incoming calls in theprescribed time interval.
 31. A method according to claim 30 furthercomprising the step of generating a signal representative of astatistical parameter of the initiation time differences in theprescribed time interval responsive to the initiation time differencessignal.
 32. A method according to claim 31, wherein the statisticalparameter signal is an average of the initiation time differences in theprescribed time interval.
 33. A method according to claim 25, furthercomprising the step of detecting a time at which the all communicationlines busy state is terminated, and the forming of the blocked incomingcalls signal comprises generating a signal corresponding to a number ofthe blocked calls responsive to the difference between the initiationand termination times of the all communication lines busy state and thecalling pattern signal.
 34. A method according to claim 33, wherein thestep of generating the number of blocked calls signal comprises forminga signal representing the difference between the initiation andtermination times of the all communication lines busy state divided bythe calling pattern signal.
 35. A method according to claim 34, whereinthe step of detecting the times of the incoming callscomprises:determining a prescribed time interval; and detecting thetimes of the incoming calls in the prescribed time interval.
 36. Amethod according to claim 34, wherein the step of detecting the times ofthe incoming calls in the prescribed time interval comprises detectingthe times at which the incoming calls are initiated in the prescribedtime interval.
 37. A method according to claim 36, wherein the step ofgenerating the calling pattern signal comprises forming a signalcorresponding to the differences in the detected initiation times ofsuccessive ones of the incoming calls in the prescribed time interval.38. A method according to claim 37, wherein the step of forming theinitiation time differences signal comprises forming a signalrepresentative of an average of the initiation time differences in theprescribed time interval.
 39. A method according to claim 25, furthercomprising the step of generating line status signals by coupling to thecommunication lines, and wherein the detecting the initiation time ofthe state in which all communication lines are busy and the incomingcall time detecting are responsive solely to the generated line statussignals.
 40. A method for monitoring a communication system having oneor more communication lines comprising the steps of:detecting times ofincoming calls on at least one of the one or more communication lines;generating a signal corresponding to a calling pattern of incoming callsresponsive to the detected times of the incoming calls; detecting a timeat which a state in which all communication lines are busy is initiated;and forming a signal representative of a time of occurrence of a blockedcall responsive to the detected initiation time of the all communicationlines busy state and the calling pattern signal.
 41. A method accordingto claim 40, wherein the step of detecting the times of the incomingcalls comprises:determining a prescribed time interval; and detectingthe times of the incoming calls in the prescribed time interval.
 42. Amethod according to claim 41, wherein the step of detecting the times ofthe incoming calls comprises detecting the times at which the incomingcalls are initiated in the prescribed time interval.
 43. A methodaccording to claim 42, wherein the step of generating the callingpattern signal comprises forming a signal corresponding to thedifferences in initiation times of the successive incoming calls in theprescribed time interval.
 44. A method according to claim 43, whereinthe step of generating the calling pattern signal further comprising thestep of generating a signal representative of a statistical parameter ofthe initiation time differences in the prescribed time intervalresponsive to the initiation time differences signal.
 45. A methodaccording to claim 44, wherein the statistical parameter signal is anaverage of the initiation time differences in the prescribed timeinterval.
 46. A method according to claim 45, wherein the step offorming the signal representative of the time of occurrence of a blockedcall comprises generating a signal at a time corresponding to theaverage of the initiation times differences in the prescribed timeinterval after the detected initiation of the all communication linesbusy state.
 47. A method according to claim 40, wherein the step offorming the signal representative of the time of occurrence of a blockedcall comprises generating a signal at a time corresponding to a value ofthe calling pattern signal after the detected initiation of the allcommunication lines busy state.
 48. A method according to claim 40,further comprising the step of generating line status signals bycoupling to the communication lines, and wherein the detecting of theinitiation time of the state in which all communication lines are busyand the incoming call time detecting are responsive solely to thegenerated line status signals.
 49. A method for estimating incomingcalls blocked as a result of all lines of a communication system beingbusy comprising the steps of:determining the rate of incoming calls;determining a time interval in which all lines are in use; and formingan estimate of blocked calls during the time interval in which all linesare in use responsive to the determined time interval and the incomingcall rate.
 50. A method according to claim 49, wherein the incoming callrate determining step comprises determining the rate of incoming callsin a time period prior to a starting time of all lines being in use. 51.A method according to claim 50, wherein the step of determining the rateof incoming calls in the time period prior to the starting of all linesbeing in use comprises forming a signal representative of thedifferences in starting times of successive incoming calls in the timeperiod and generating a signal corresponding to the average startingtime difference in the time period.
 52. A method according to claim 50,wherein the step of determining the incoming call rate in the timeperiod comprises forming a signal representative of the average incomingcall rate in a prescribed time period just preceding the start of thetime interval in which all lines are in use.
 53. A method according toclaim 52, wherein the step of forming an estimate of blocked callscomprises dividing the time interval in which all lines are in use bythe average incoming call rate.